1. Technical Field
The present invention relates to an assembly structure of a bearing and a holder of a brushless DC motor.
2. Description of the Related Art
Generally, brushless DC motors have an electronic commutation device, instead of having mechanical contact parts, such as a brush and a commutator, which are provided in a DC motor to alternately supply current. The brushless DC motors are also called commutatorless motors.
Such a brushless DC motor includes a bearing and a holder. The bearing supports a shaft such that it is prevented from being displaced from its proper center axis when the motor is operated. The holder supports the bearing. Typically, the bearing is assembled with the holder in such a way as to forcibly fit the bearing into a hollow space formed through the holder.
FIGS. 1A and 1B are sectional views showing the assembly of a bearing 200 with a holder 100 of a brushless DC motor according to a conventional technique.
As shown in FIGS. 1A and 1B, in the conventional technique, the holder 100 has a hollow space 110 which defines a circumferential inner surface 112 which is planar for its entire length. The bearing 200 has a circumferential outer surface 210 which is planar for its entire length. The bearing 200 is assembled with the holder 100 in such a manner that after the bearing 200 is disposed above the holder 100 (refer to FIG. 1A), the bearing 200 is forcibly fitted into the hollow space 110 of the holder 100 (refer to FIG. 1B). Here, even if just a minute space is present between the bearing 200 and the holder 100, the shaft is displaced from the center axis thereof. To avoid this problem, the holder 100 and the bearing 200 are configured such that the outer diameter of the bearing 200 is almost the same as the inner diameter of the holder 100.
However, in the case where the outer diameter of the bearing 200 is the same as the inner diameter of the holder 100, it becomes difficult to forcibly fit the bearing 200 into the hollow space 110 of the holder 100. In particular, when a mouth edge 120a of the holder 100 through which the bearing 200 enters the holder 100 has a planar structure (a vertical cross-section in the drawings), it is very difficult even to align the bearing 200 with the mouth edge 120a of the holder 100. Furthermore, in this state, when the bearing 200 is forcibly fitted into the holder 100, a bun occurs on the mouth edge 120a of the holder 100, resulting in requiring an additional machining process for removing the burr.